Vaccum Mystery possibly solved

[GusMcRae]

Long story short,,, wound up isolating the problem to the DG (which was sent off in Feb or so of 2013, returned saying everything was AOK, no problems found,,,,) and discovered this crack in the female threaded inlet housing.  I'm pretty sure this is where my problem is.  If you are able to zoom the picture, you can see how far the crack goes down.  Actually after looking at it after posting it, you can see it just fine.
Not sure if it was already cracked when we sent it in a year ago,,, or if the MX that removed it and re-installed it, screwed the tube so far in that it split the housing. 



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[Flying Razorback]

Wow that's some good investigating work.  I hope it's easy to fix and stays that way for you.

[GusMcRae]

Called the shop that did the repair last year to see how much it cost to replace that piece.  $30.   They say this happens all the time, they see them come in for repair that have been siliconed, taped, glued, etc...  Although it's been a little over a year (which is how long the warranty was good for), he will replace the piece for $30, won't charge me any labor, and will re-check it after replacing to make sure it all checks out good.  I'll have the cost of freight in there too.  If I still have a vaccum problem when I get it back and installed, I'll know it's not the DG.  Makes perfect sense to me that this is the problem.  Sent it off today, so probably won't get it back until mid to late week next week. 

[gotyacovered]

Frustrating, but nice to isolate it. If it isn't the culprit, at least it was easy/cheap fix.

[GusMcRae]

Frustrating, but nice to isolate it. If it isn't the culprit, at least it was easy/cheap fix.

And I keep learning things every time we work through one of these little problems.

[gotyacovered]

And I keep learning things every time we work through one of these little problems.

sounds familiar. be nice to quit learning so much, though, wouldnt it

[GusMcRae]

sounds familiar. be nice to quit learning so much, though, wouldnt it

It sure would. 
It sure would be nice to go for a long stretch of trouble free flying.
I've had my cowling off so many times, I think I could take it off and put it back on blindfolded.

[gotyacovered]

It sure would. 
It sure would be nice to go for a long stretch of trouble free flying.
I've had my cowling off so many times, I think I could take it off and put it back on blindfolded.

I could do blindfolded, but give me a time limit and I'm in trouble!

[Warbirdhog]

Odds are that is your problem.  Fittings have to be seated with care into those cases, they can't be forced tight. Anytime I have one that won't clock into the needed position without I'll get another fitting and try it if I have one available. Usually works as the threads from fitting to fitting are different most of the time where they start and stop.
I also use teflon paste instead of tape as it gives a better thread seal. The fittings don't really have to be much more than hand tight, our Curtiss P-40 manuals actually give torque settings for pipe threads. You would be surprised at how low the torque is for them.

[GusMcRae]

Anytime I have one that won't clock into the needed position without I'll get another fitting and try it if I have one available. Usually works as the threads from fitting to fitting are different most of the time where they start and stop.
I also use teflon paste instead of tape as it gives a better thread seal. The fittings don't really have to be much more than hand tight, our Curtiss P-40 manuals actually give torque settings for pipe threads.

Just FYI, I put that teflon tape on there after I discovered it was split, and while we were considering rigging it some kind of way with tape or silicone.  Have since been advised not to use teflon tape.  When I found out how inexpensive it was going to be to have the back plate replaced, and that they would bench test it again, I went that route.  I got a call yesterday that repair was done, checked out fine, and it's being shipped back.  I figure it will be here tomorrow.  Thanks for the tip about teflon paste.  I had included a note asking what to use for sealant when I sent it off. 

[Warbirdhog]

Tape isn't good to use, just doesn't give the seal of a paste thread sealant and there is always the risk of the threads cutting the tape.  Just be careful when installing the fitting and don't force it when clocking it to the direction you need it to be in.


Gus, I did not think to post what I use. The paste I use is La-Co Slic Tite,  IIRC it came from McMaster Carr.

[GusMcRae]

Got the DG re-installed and took it for a test flight over the weekend.  Did 3 night TO and landings to get current and after that much turning, DG was still right on the money of where I set it when I started.  Suction gauge was back where it's supposed to be as well.  I'm fairly confident this lingering problem has been resolved. 

Time to get back to IFR training.

[gotyacovered]

Got the DG re-installed and took it for a test flight over the weekend.  Did 3 night TO and landings to get current and after that much turning, DG was still right on the money of where I set it when I started.  Suction gauge was back where it's supposed to be as well.  I'm fairly confident this lingering problem has been resolved. 

Time to get back to IFR training.

great news, glad to hear.